Biology. A single-celled organism, esp. a protozoan; spec. a flagellate protozoan of the genus Monas, the former family Monadinidae (or Monadidae)…

= primigenial, adj. 2.

Zoology. = primigenial, adj. 2. Now rare.

Primeval, primigenial; (Biology, now historical) designating a former kingdom of living organisms proposed by J. Hogg and named Regnum Primigenum…

Zoology. Designating or relating to a species or variety regarded as an evolutionary ancestor of a related modern form.

Of or relating to the kingdom Protista; protistan.

Geology. Designating the geological period from which there are no present-day remains of animals then existing, and the animals themselves. Cf. Crypt…

Zoology and Archaeology. Primigenial (primigenial, adj. 2); spec. designating or characteristic of the aurochs, Bos primigenius.